1. Incorporation by Reference
The following commonly assigned applications are co-pending with this application and are hereby incorporated by reference:
Ser. No. 210,892, filed Jun. 24, 1988 "MEASUREMENT OF THERMAL CONDUCTIVITY AND SPECIFIC HEAT", U.S. Pat. No. 4,944,035; Ser. No. 211,014, filed Jun. 24, 1988, entitled "MEASUREMENT OF FLUID DENSITY", U.S. Pat. No. 4,956,793.
Ser. No. 285,897, filed Dec. 16, 1988 entitled entitled "FLOWMETER FLUID COMPOSITION CORRECTION", U.S. Pat. No. 4,961,348; Ser. No. 285,890, filed Dec. 16, 1988 entitled "LAMINARIZED FLOWMETER" abandoned.
2. Field of the Invention
The present invention relates to controlling the combustion process for a heating system. More particularly, the present invention relates to controlling a fuel-to-air ratio of that combustion process.
3. Description of the Prior Art
There are many applications for industrial and commercial heating systems such as ovens, boilers and burners. These heating systems are generally controlled by some type of control system which operates fuel valves and air dampers to control the fuel-to-air ratio which enters the heating system. It is generally desirable to sense the fuel-to-air ratio to achieve a desired combustion quality and energy efficiency.
Conventional sensing of the fuel-to-air ratio has taken two forms. The first form includes sensing the concentration of carbon dioxide or oxygen in flue gases. This method of sensing the proper fuel-to-air ratio is based on an intensive measurement of the flue gases. However, in practice, this method has encountered problems of reliability due to inaccuracy in the sensors which are exposed to the flue gases. Problems related to response time of the sensors have also been encountered. The system cannot sense the carbon dioxide and oxygen components of the flue gasses and compute the fuel-to-air ratio quickly enough for the fuel and air flow to be accurately adjusted.
The second form includes monitoring the flow rate of the fuel and air as it enters the burner. This method leads to a desirable feed-forward control system. However, until now, only flow rate sensors have been involved in this type of monitoring system. Therefore, the system has been unable to compensate for changes in air humidity or fuel composition.